U.S. patent number 7,219,021 [Application Number 11/317,706] was granted by the patent office on 2007-05-15 for multiple wireless sensors for dialysis application.
This patent grant is currently assigned to Honeywell International Inc.. Invention is credited to Alistair D. Bradley, James D. Cook, James Z T Liu, Gautham Ramamurthy, Stephen R. Shiffer.
United States Patent |
7,219,021 |
Liu , et al. |
May 15, 2007 |
**Please see images for:
( Certificate of Correction ) ** |
Multiple wireless sensors for dialysis application
Abstract
A sensor system for dialysis applications includes a plurality
of pressure sensors, wherein each pressure sensor can be provided
as an LC type sensor, and/or an RLC type sensor. Each sensor among
the plurality of pressure sensors can be inductively coupled with a
respective antenna among a plurality of antennas for the wireless
transmission of pressure data. A dialysis machine is generally
connected to the plurality of antennas, wherein the plurality of
pressure sensors monitors pressure during operation of the dialysis
machine to generate pressure data that is wirelessly transmitted to
at least one antenna among the plurality of antennas.
Inventors: |
Liu; James Z T (Hudson, NH),
Ramamurthy; Gautham (Bangalore, IN), Bradley;
Alistair D. (Dublin, OH), Cook; James D. (Freeport,
IL), Shiffer; Stephen R. (Xenia, OH) |
Assignee: |
Honeywell International Inc.
(Morristown, NJ)
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Family
ID: |
37856368 |
Appl.
No.: |
11/317,706 |
Filed: |
December 24, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070061089 A1 |
Mar 15, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11242271 |
Oct 3, 2005 |
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11226085 |
Sep 13, 2005 |
7181975 |
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Current U.S.
Class: |
702/50 |
Current CPC
Class: |
A61M
1/3639 (20130101); A61M 1/14 (20130101); A61M
2205/3592 (20130101); A61M 2205/3569 (20130101) |
Current International
Class: |
G01F
17/00 (20060101) |
Field of
Search: |
;702/50 ;600/549,561
;73/718 ;604/4.01 ;370/278 ;324/318 ;435/4 ;343/895 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 02/22187 |
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Mar 2002 |
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WO |
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WO 02/085040 |
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Oct 2002 |
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WO |
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WO 2004/078463 |
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Jan 2004 |
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WO |
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Primary Examiner: Barlow; John
Assistant Examiner: Sun; Xiuqin
Attorney, Agent or Firm: Lopez; Kermit D. Ortiz; Luis M.
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
This patent application is a Continuation-In-Part (CIP) of U.S.
patent application Ser. No. 11/242,271, entitled "Wireless Pressure
Sensor and Method Forming the Same," which was filed on Oct. 3,
2005, and is incorporated herein by reference in its entirety. This
patent application is also a Continuation-In-Part (CIP) of U.S.
patent application Ser. No. 11/226,085, entitled "Wireless
Capacitance Pressure Sensor," which was filed on Sep. 13, 2005, now
U.S. Pat. No. 7,181,975, and is incorporated herein by reference in
its entirety.
Claims
What is claimed is:
1. A sensor system for dialysis applications, comprising: a
plurality of pressure sensors, wherein each pressure sensor among
said plurality of pressure sensors comprises an
inductive-capacitive tank circuit such that said plurality of
pressure sensors is inductively coupled respectively to a plurality
of coil antennas for the wireless transmission of pressure data,
wherein each coil antenna among said plurality of coil antennas
comprises a planar coil surrounded by a shielding ring; and a
dialysis machine connected to said plurality of coil antennas,
wherein said shielding ring comprises metallized plastic with an
electrical connection to a ground located within said dialysis
machine and wherein said plurality of pressure sensors monitors
pressure during an operation of said dialysis machine to generate
pressure data that is wirelessly transmitted to at least one
antenna among said plurality of coil antennas.
2. The system of claim 1 further comprising: a plurality of
oscillator circuits associated with said plurality of coil
antennas; a plurality of low frequency switches associated with
said plurality of oscillator circuits; and an electronics module
for operating said switches and for processing said pressure data
generated by said plurality of pressure sensors.
3. The system of claim 2 wherein each oscillator circuit among said
plurality of oscillator circuits comprises a Grip Dip Oscillator
(GDO), and said electronics module comprises a microcontroller.
4. The system of claim 3 wherein said GDO comprises an oscillator
that produces an output signal that is input to a level shifter,
which in turn produces an output signal which is input to a
low-pass filter, which in turn produces a DC output signal.
5. The system of claim 1 wherein each pressure sensor among said
plurality of pressure sensors operates within a different resonant
frequency band.
6. The system of claim 1 wherein each pressure sensor among said
plurality of pressure sensors operates within a same or an
overlapping resonant frequency band.
7. The system of claim 1 wherein at least one pressure sensor among
said plurality of pressure sensors is located in at least one of
the following positions within said dialysis machine: an arterial
line, a dialyzer line, or a venous line.
8. A sensor system for dialysis applications, comprising: a
plurality of pressure sensors, wherein each pressure sensor among
said plurality of pressure sensors comprises at least one of the
following types of sensors: an LC (Inductance-Capacitance) type
sensor, an RLC (Resistance-Inductance-Capacitance) type sensors or
a combination thereof, and wherein each pressure sensor among said
plurality of pressure sensors is coupled with at least one antenna
for the wireless transmission of pressure data, wherein each
antenna among said plurality of antennas comprises a planar coil
surrounded by a shielding ring; and a dialysis machine connected to
said antenna, wherein said shielding ring comprises metalized
plastic with an electrical connection to a ground located within
said dialysis machine and wherein said plurality of pressure
sensors monitors pressure during operation of said dialysis machine
to generate pressure data that is wirelessly transmitted to said
antenna.
9. The system of claim 8 further comprising: a plurality of
oscillator circuits associated with said plurality of pressure
sensors and said at least one antenna; a plurality of low frequency
switches associated with said plurality of oscillator circuits; and
an electronics module for controlling a plurality of low frequency
switches and for processing said pressure data generated by said
plurality of pressure sensors.
10. The system of claim 9 wherein at least one pressure sensor
among said plurality of pressure sensors is located in at least one
of the following positions within said dialysis machine: an
arterial line, a dialyzer line, or a venous line.
11. A sensor system for dialysis applications, comprising: a
plurality of pressure sensors, wherein each pressure sensor among
said plurality of pressure sensors comprises an LC
(Inductance-Capacitance) tank sensor and is inductively coupled to
a respective antenna among a plurality of antennas for the wireless
transmission of pressure data wherein each antenna among said
plurality of antennas comprises a planar coil surrounded by a
shielding ring; a dialysis machine connected to said plurality of
antennas, wherein said shielding ring comprises metalized with an
electrical connection to a round located within said dialysis
machine and wherein said plurality of pressure sensors monitors
pressure during an operation of said dialysis machine to generate
pressure data that is wirelessly transmitted to at least one
antenna among said plurality of antennas; a plurality of oscillator
circuits associated with said plurality of antennas; a plurality of
low frequency switches associated with said plurality of oscillator
circuits; and an electronics module for operating said plurality of
low frequency switches and processing said pressure data generated
by said plurality of pressure sensors.
12. The system of claim 11 wherein each pressure sensor among said
plurality of pressure sensors operates within a different resonant
frequency band.
13. The system of claim 11 wherein each pressure sensor among said
plurality of pressure sensors operates within a same or an
overlapping resonant frequency band.
14. The system of claim 11 wherein each oscillator circuit among
said plurality of oscillator circuits comprises a GDO.
15. The system of claim 11 wherein at least one pressure sensor
among said plurality of pressure sensors is located in at least one
of the following positions within said dialysis machine: an
arterial line, a dialyzer line, or a venous line.
16. A sensor system for dialysis applications, comprising: a
plurality of pressure sensors, wherein each pressure sensor among
said plurality of pressure sensors comprises an
inductive-capacitive tank circuit such that said plurality of
pressure sensors is inductively coupled respectively to a plurality
of coil antennas for the wireless transmission of pressure data;
and a plurality of oscillator circuits associated with said
plurality of coil antennas; a plurality of low frequency switches
associated with said plurality of oscillator circuits; an
electronics module for operating said switches and for processing
said pressure data generated by said plurality of pressure sensors,
wherein each oscillator circuit among said plurality of oscillator
circuits comprises a Grip Dip Oscillator (GDO), and said
electronics module comprises a microcontroller, wherein said GDO
comprises an oscillator that produces an output signal that is
input to a level shifter, which in turn produces an output signal
which is input to a low-pass filter, which in turn produces a DC
output signal; and a dialysis machine connected to said plurality
of coil antennas, wherein said plurality of pressure sensors
monitors pressure during an operation of said dialysis machine to
generate pressure data that is wirelessly transmitted to at least
one antenna among said plurality of coil antennas.
17. The system of claim 16 wherein at least one pressure sensor
among said plurality of pressure sensors Is located in an arterial
line associated with said dialysis machine.
18. The system of claim 16 wherein at least one pressure among said
plurality of pressure sensors is located in a dialyzer line
associated with said dialysis machine.
19. The system of claim 16 wherein at least one pressure among said
plurality of pressure sensors is located in a venous line
associated with said dialysis machine.
20. The system of claim 16 wherein each pressure sensor among said
plurality of pressure sensors operates within a different resonant
frequency band.
21. The system of claim 16 wherein each pressure sensor among said
plurality of pressure sensors operates within a same or an
overlapping resonant frequency band.
Description
TECHNICAL FIELD
Embodiments are generally related to sensing devices and methods.
Embodiments are also related to wireless sensors. Embodiments are
additionally related to dialysis applications and pressure sensors
for use in monitoring pressure during a dialysis application.
BACKGROUND OF THE INVENTION
Sensors are utilized in a number of applications, including various
medical, commercial and industrial applications. For example, it is
often necessary to monitor pressure and/or to detect flow rates in
medical applications and processes.
One area where pressure sensors, for example, find particular
usefulness is in the area of hemodialysis applications. In such
medical procedures, a dialysis machine is utilized to clean wastes
from the blood after the kidneys have failed. The blood travels
through tubes to a dialyzer, a machine that removes wastes and
extra fluid. The cleaned blood then goes back into the body.
A known-type dialysis machine comprises a first blood circulation
circuit and a second circulation circuit for the dialysate liquid.
The first circuit and the second circuit are connected to a filter
for conveying, respectively, the blood and dialysate liquid through
the filter, which is provided with a semi-permeable membrane
separating the blood from the dialysate liquid. The first circuit
is provided with a container, known as a drip chamber, into which
the blood is supplied from a first tract of the first circuit, and
drips and collects on the bottom of the container, thence to enter
a second tract of the first circuit.
The container has the function of preventing air from becoming
trapped in the blood in the form of bubbles, which might cause
embolisms once the treated blood is returned to the cardiovascular
system of the patient. To guarantee the safest possible treatment
the blood level in the container must be maintained within an
optimum range of values, below which the possibility of creating
air bubbles in the blood returning to the patient exists, and above
which the pressure increases to unacceptable values which are
dangerous for the patient. Thus, the ability to monitor pressure in
such a setting is critical to a proper, safe, and successful
dialysis treatment.
One type of dialysis application is disclosed in U.S. Pat. No.
6,695,806, entitled "Artificial Kidney Set with Electronic Key,"
which issued to Gefland et al on Feb. 24, 2004 and is incorporated
herein by reference. Another type of dialysis application is
disclosed in U.S. Pat. No. 6,887,214, entitled "Blood Pump Having a
Disposable Blood Passage Cartridge with Integrated Pressure
Sensors," which issued to Levin et al on May 3, 2005 and is
incorporated herein by reference. It can be appreciated that U.S.
Pat. Nos. 6,695,806 and 6,887,214 are referenced herein for general
background and edification purposes only and are not considered
limiting features of the embodiments described herein.
Dialysis machines historically have utilized sets of disposable
components that are assembled from various parts produced by
different manufacturers. This allowed flexibility, but also
resulted in certain disadvantages. Joints between component parts,
for example, may leak, allow ingress of air and facilitate blood
clotting. A high skill was required by hospital nurses and
technicians to assemble the tubes, connectors, filters and
accessories and then load them correctly into pumps, bubble
detectors, pressures sensors and other elements of a dialysis
machine. In the setting of a chronic dialysis center such practices
were acceptable. In an acute setting, however, such an Intensive
Care Unit (ICU) of a hospital, the complexities of dialysis
machines can become an impediment.
As a result, the use of mechanical fluid removal in the ICU,
emergency rooms and general floors of a hospital has been limited.
Some manufacturers have released sophisticated dialysis equipment
based on the use of an integrated set of disposable dialysis
components in which the tubing, filter and accessories are bonded
together and no assembly is required. In such a device, the filter,
sensor interfaces and four dedicated pump segments (for blood,
dialysate, replacement solution and effluent) can be mounted on a
flat plastic cartridge to simplify the loading of the dialysis
pumps. Such a dialysis system has been marketed as offering an
integrated system for continuous fluid management and automated
renal replacement therapy blood.
While such devices do offer significant advantages, such equipment
also has a number of deficiencies. One deficiency is that although
such systems provide for a set of disposable dialysis components
that are continuous and bonded together, the system does not
present a smooth blood path, but incorporates elements that create
stagnant and slow moving blood zones. In such blood zones clots are
likely to form. Such devices may also employ an interface to
pressure sensors that is relatively inaccurate, unreliable and
requires maintenance. There is thus a need for an improved design
of the blood flow dialysis set that is simple to use, requires no
maintenance or special training, and also has an improved
performance over existing sets of disposable components utilized in
such dialysis machines.
Additionally, such dialysis machines do not integrate pressure
sensors. Instead, these types of dialysis devices integrate
pressure "pods" shaped as domes. The interface surface of a pod can
be made from a silicon membrane approximately one inch in diameter.
When mounted on such a dialysis machine, the pods interface with
the permanently installed pressure sensors that form a part of the
machine. The interface is sealed by a rubber gasket so that the pod
membrane serves as a lid on the pressure transducer cavity. When in
operation, blood and other fluids flow through the pods and come in
contact with the membrane.
Pressure pods provide a means to measure the pressure of blood and
other fluids flowing outside an interface surface. When the
pressure inside the pod is increased, the diaphragm stretches and
thereby compresses the air inside a transducer cavity. As a result,
pressure in the bloodline or a fluid line can be measured. The pod
membrane serves as a barrier between the blood and potential
contamination from the environment, as is similar to the clinical
invasive vascular blood pressure measurements. This method,
although functional, has several deficiencies.
First, to be accurate such pods need to be positioned perfectly
when the pressure inside is atmospheric. Over time, if there is
even a miniscule leak on the transducer side of the membrane, the
pod will creep and gradually stop transmitting pressure accurately
because of the tension in the membrane. Second, stretchable
membranes and air filled transducer cavities add compliance to the
circuit. Compliance is a delay in a pressure measurement due to the
time required to stretch the pods and compress the air inside the
pod cavity. Compliance is not desired since it makes the system
less responsive to controls.
Third, pods filled with blood increase the blood-plastic contact
surface and create stagnant zones with low blood flow velocity that
facilitate clot formation. Because the clots may form in the pods,
the use of pods also necessitates the use of clot capture devices.
Fourth, pod domes have a significant volume that increases the time
that blood spends in contact with foreign materials. Altogether
this increases the risk of blood loss, hypotension and
clotting.
In order to address the needs of fluid removal and dialysis in
acute emergency settings and to eliminate significant limitations
of existing designs, it is believed that an improved sensor system
should be adapted for use with dialysis machines. It is believed
that the improved multiple sensor system disclosed herein can
address these and other continuing needs.
BRIEF SUMMARY
The following summary is provided to facilitate an understanding of
some of the innovative features unique to the embodiments disclosed
and is not intended to be a full description. A full appreciation
of the various aspects of the embodiments can be gained by taking
the entire specification, claims, drawings, and abstract as a
whole.
It is, therefore, one aspect of the present invention to provide
for an improved sensor system.
It another aspect of the present invention to provide for an
improved pressure sensor system for use in dialysis
applications.
It is yet another aspect of the present invention to provide for a
sensor system that avoids the need for both careful mechanical
alignment and electrical connection between the sensor and dialysis
machine. A further aspect of the present invention is to provide
for a reduced sensor size that permits reduced contact volume and
dead-space in a sensing application.
The aforementioned aspects and other objectives and advantages can
now be achieved as described herein. A sensor system for dialysis
applications is disclosed, which includes a plurality of passive
resonant circuit pressure sensors inductively coupled to a
plurality of antennas. Wherein each sensor among the plurality of
pressure sensors is implemented as inductive-capacitive (LC)
resonant circuit (tank) sensors associated with a respective
antenna among the plurality of antennas for the wireless
transmission of pressure data. A dialysis machine is generally
connected to the plurality of pressure sensors and the plurality of
antennas, wherein the plurality of pressure sensors monitors
pressure during a dialysis operation of the dialysis machine to
generate pressure data that is wirelessly transmitted from at least
one antenna among the plurality of antennas.
A plurality of oscillator circuits is also associated with the
plurality of pressure sensors and the plurality of antennas.
Additionally, a plurality of low frequency switches is associated
with the plurality of oscillator circuits. An electronics
processing module is also provided for processing the pressure data
generated by one or more of the pressure sensors, while each
oscillator circuit among the plurality of oscillator circuits can
be implemented as a Grid Dip Oscillator (GDO). Each GDO can be
configured to include an oscillator component that produces an AC
output signal that is input to a level shifter, which in turn
produces an output signal that has either the negative or positive
signal peak clamped to a fixed reference level. This signal is then
input to a low-pass filter, which in turn produces a DC output
signal. The DC output signal from the filter is thus proportional
to the peak-to-peak signal from the oscillator. In this way the use
of RF switch is avoided for multiple sensor concepts.
Each antenna can be provided as a planar coil surrounded by a
shielding ring. The shielding ring can be configured in the form of
metalized plastic with an electrical connection to ground within
the dialysis machine. Each pressure sensor can be implemented as an
LC tank sensor and can be located in at least one of the following
positions within the dialysis machine: an arterial line, a dialyzer
line, or a venous line, depending upon design considerations. Each
sensor may operate within different resonant frequency bands from
one another or within the same or overlapping frequency bands,
depending on design goals and considerations.
An alternative embodiment involves the use of wireless LC tank
multiple sensors in the context of a sensor system in which the
sensors share a single antenna. Multiple capacitors, each of which
forms a variable C component in the LC tank sensor, can be linked
with a single planar coil, such that each associated variable
capacitor results in a pressure dependent signature frequency
(i.e., spurs). Multiple frequencies can exist in such a system
through prudent design. The amplitudes of the spurs can be
maximized for ease of detection.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying figures, in which like reference numerals refer to
identical or functionally-similar elements throughout the separate
views and which are incorporated in and form a part of the
specification, further illustrate the embodiments and, together
with the detailed description, serve to explain the embodiments
disclosed herein.
FIG. 1 illustrates a high-level view of the left side of a
conventional kidney dialysis machine, which can be adapted for use
in accordance with one or more embodiments;
FIG. 2(a) illustrates a system of reader antennas reader antenna,
which can operate in overlapping frequency bands about the same
`zero pressure differential` resonant frequency, f.sub.0, in
accordance with a first embodiment;
FIG. 2(b) illustrates a graph depicting how the system illustrated
in FIG. 2(a), can operate at different resonant frequencies, in
accordance with an alternative version of the first embodiment;
FIG. 3 illustrates a block diagram depicting a sensor system, which
can be implemented in accordance with a preferred embodiment;
FIG. 4 illustrates a block diagram depicting components that can be
utilized to implement an example oscillator circuit in accordance
with an alternative, but first embodiment;
FIG. 5 illustrates a block diagram of a multiple sensor system for
use in dialysis applications, in accordance with an alternative
first embodiment;
FIG. 6 illustrates a block diagram of a multiple sensor system for
use in dialysis applications, in accordance with another version of
the embodiment depicted in FIG. 5;
FIG. 7 illustrates a graph depicting a variety of frequencies in
the context of a sensor system for dialysis applications, in
accordance with a second embodiment;
FIG. 8 illustrates a sensor system based on a plurality of circular
electrodes forming a plurality of variable capacitors, in
accordance with the second embodiment; and
FIG. 9 illustrates a schematic diagram of an example equivalent
circuit of the configuration depicted in FIG. 8.
DETAILED DESCRIPTION
The particular values and configurations discussed in these
non-limiting examples can be varied and are cited merely to
illustrate at least one embodiment and are not intended to limit
the scope thereof.
FIG. 1 illustrates a high-level view of the left side of a
conventional kidney dialysis machine 110, which can be adapted for
use in accordance with one or more embodiments. The dialysis
machine 110 generally includes a machine housing 111 that contains
a membrane apparatus (not shown) for performing dialysis. The
illustrated dialysis machine 110 can also include a threaded shaft
112 extending from the back of the housing 111. The shaft 112 can
be located near the top of the housing and a knob 114 can be
threaded on the shaft 112.
The housing is generally mounted on wheels 115 that support the
housing on the floor of a patient station. It can be appreciated
that the dialysis machine 110 depicted in FIG. 1 represents one of
many possible dialysis machines that can be utilized in accordance
with the embodiments disclosed herein. As such, the dialysis
machine 110 illustrated in FIG. 1 is not considered a limiting
feature of the disclosed embodiments. Rather, dialysis machine 110
is presented for general edification and exemplary purposes only.
It can be appreciated that the embodiments disclosed herein can be
practiced not only in the context of dialysis applications, but
also in the context of non-dialysis applications, such as, for
example, external blood treatment applications.
FIG. 2(a) illustrates a system 200 of antenna 201, 203, 205, which
can operate at the same zero pressure resonant frequency, f.sub.0,
in accordance with a first possible embodiment. System 200 depicted
in FIG. 2(a) can be adapted for use with the dialysis machine 110
depicted in FIG. 1. Sensors (not shown in FIG. 2(a), but
illustrated in FIGS. 3, 5 and 6) can be implemented as LC tank
sensors in association with system 200 with either L varying with
pressure or C or both L and C varying with pressure depending upon
design considerations. Such sensors are illustrated in greater
detail herein with respect to FIGS. 3 6.
In the configuration of system 200, shielding rings 202, 204, 206
respectively surround and screen one side of one or more of the
coil antennas 210, 208, and 212. When utilized in the context of a
system that includes a Radio Frequency (RF) switch 228, the set of
three antennas 201, 203, 205 can make use of the same frequency
range for sensing applications. A graph 220 depicted in FIG. 2(a)
illustrates a representative x-ordinate frequency range. In graph
220, a central zero pressure frequency f.sub.0 is shown with
pressure values 222, 224, and 226 (i.e., P.sub.1, P.sub.2, P.sub.3)
varying the resonant frequency associated with three different
sensors. Thus, FIG. 2 illustrates detection of resonant frequencies
about a common zero-pressure frequency using multiple interrogation
coil antenna 210, 208, 212.
FIG. 2(b) illustrates a graph 231 depicting how a system of sensors
(e.g., see sensors 402, 404, 406 in FIGS. 5-6 and sensors 330, 344
in FIG. 3) can operate in different resonant frequency bands, in
accordance with an alternative version of the first embodiment.
Note that in FIGS. 2(a) 2(b) identical or similar elements or
components are generally indicated by identical reference numerals.
Thus, zero pressure frequencies, f.sub.0, f.sub.02, and f.sub.03
are shown along the x-ordinate frequency range 230 in FIG.
2(b).
FIG. 2(b) indicates that multiple LC tank sensors can operate in
different resonant frequency bands to avoid interference between
different sensor and antenna signals. Single or multiple
interrogation electronics, such as, for example, Grid Dip
Oscillator (GDO) circuits, can be utilized depending on the
available dynamic range of the GDO circuit. In other words, GDO
circuits can be utilized if the frequency range over which the
oscillator circuit operates can sustain oscillations. In either
case, single or multiple antenna configurations can be implemented,
depending on the strength of the inductive coupling of each of the
sensors to the antenna(s). The embodiment depicted in graph 220 of
FIG. 2(a) uses sensors operating in the same frequency resonant
frequency band and multiple interrogation antenna 201, 203, 205
separated from one another and preferably with the respective
shielding 202, 204, 206 around each coil 210, 208, 212.
Note that the RF signal from the antenna coils 210, 208, 212 can be
focused and/or limited to respective sensors directly facing the
antenna, while signals radiated to other sensors not directly
facing the antenna coil can be completely shielded or significantly
reduced. Where necessary RF switches such as RF switch 228 depicted
in FIG. 1 can be used to switch the supply and/or output signals
from utilized GDO circuits.
Assuming that it is desired to implement a system in which the
sensors operate within different frequency bands (e.g., see graph
231 of FIG. 2(b)); one or more GDO circuits should be utilized,
which operate over the widest range frequencies. Such a
configuration can be implemented with a single antenna coil and a
GDO with a wide dynamic range. In order to obtain the detection
sensitivity required, however, the change in resonant frequency of
a single sensor (i.e., with pressure) may already reach the limits
of the GDO's dynamic range. Thus, multiple antennas with multiple
GDO circuits may be required. Alternatively, where sensors operate
within the same frequency band, multiple antennas may also be
required to physically differentiate between the sensors (e.g., see
FIG. 2(a)).
Each antenna coil 210, 208, 212 can take the form of a planar coil
based, for example, on a Printed Circuit Board (PCB) or polymer
substrate, or the form of a multi-layer PCB coil, wound Litz wire,
wound copper wire, or other similar structure. Shielding can be
implemented in, for example, metalized plastic or sheet metal, with
electrical connections to ground in the dialysis equipment of, for
example, the dialysis machine 110 depicted in FIG. 1. Preferably,
this shielding would be implemented in the same process as the coil
manufacture itself. Alternatively, a material with high
permeability could be attached, deposited and/or located nearby,
such as, for example, mu-metal, in order to stop or reduce the
field due to limited skin depth at measurement frequencies. The
diameter and height of the shielding rings 202, 204, and/or 206 can
be determined by the relative distance and the angle between
sensors and their respective antenna coils 210, 208, 212.
In the embodiments described above wherein the GDO dynamic range is
large enough, multiple sensors can be connected to one GDO with
three different antennas. In such a scenario, an RF switch such as,
for example, RF switch 228 depicted in FIG. 2(a), can be utilized
to switch between the interrogation antennas 201, 203, 205. In
embodiments where the dynamic range of the GDO is limited, multiple
GDO circuits can be linked to a single antenna using an RF switch.
Alternatively, wherein both multiple GDO circuits and antenna are
required to provide both the required operating frequency range and
coupling between sensors that are spatially separated along with
their respective antenna, two different arrangements can be
implemented, as indicated herein with respect to FIGS. 5 and 6,
which are described in greater detail below.
FIG. 3 illustrates a block diagram depicting a sensor system 300,
which can be implemented in accordance with a preferred embodiment
and in association with the antenna embodiments depicted in FIGS. 1
2(a)/(b) and FIGS. 4 6. System 300 generally incorporates the use
of multiple wireless LC tank pressure sensors for use with a
hemodialysis machine such as, for example, the dialysis machine 110
depicted in FIG. 1. System 300 includes a disposable cartridge 335
which can support one or more pressure sensors 330, 344. The
pressure sensor 330 includes a variable capacitance sensing element
332 and a sensor coil 346. Similarly, the pressure sensor 344
includes a sensing element 342 and a sensor coil 336. Inductive
coupling (electromagnetic field show schematically as 328 and 326)
are also provided, wherein the primary inductive coupling is
between the sensor coils 346 and 336 and reader coils 322 and 324
respectively.
The dialysis machine 110 can also include reader coils 322 and 324,
which are located respectively proximate to the sensor coils 346
and 336. Importantly the relative position of the sensor and reader
coils need not be precisely maintained in order to achieve wireless
transfer of pressure data, thus allowing ease of placement and
attachment of the disposable cartridge by the hospital nurses and
technicians. The dialysis machine 110 can also incorporate various
measurement and control electronics 315 which communicate with
reader electronics 314 that include a GDO 318, a GDO 320 and a
microcontroller 316. Note that each GDO 318, 320 are respectively
similar to the GDO 400 illustrated in FIG. 4. The system 300 is
illustrated as a two sensor configuration. It can be appreciated,
however, that system 300 can be modified to operate with additional
sensors, GDO circuits, and so forth.
FIG. 4 illustrates a block diagram depicting components that can be
utilized to implement an example oscillator circuit 302 in
accordance with an alternative, but first embodiment. Note that in
FIGS. 4, 5 and 6, the illustrated configurations generally depict a
DC/low frequency switch arrangement. FIGS. 5 6 generally relate to
a three sensor configuration. It can be appreciated, however, that
the system 300 depicted in FIG. 3 can be modified to operate in the
context of a three sensor configuration, such as that depicted in
FIGS. 5 6, rather than the two sensor configuration of FIG. 3. The
oscillator circuit or GDO 302 is generally composed of an
oscillator 306, which in turn generates AC signal that is sent to a
level shifter 308. The level shifter 308 ensures the signal from
oscillator is available to the low-pass filter 310 without the
influence of the DC bias voltage of the oscillator circuit 302 and
also that the output signal has either the negative or positive
signal peak clamped to a reference level. The signal strength may
be further increased by using a peak detector circuit (not shown)
and output to the low pass filter 310. The low-pass filter 310
finally generates a DC output 311 which is thus proportional to the
peak-to-peak signal from the oscillator circuit 302. The GDO 302
can be connected to an antenna 304 via connecting lines 305,
307.
Note that the antenna 304 depicted in FIG. 4 is analogous to each
of the antenna 201, 203, 205 depicted in FIG. 2(a). In other words,
one or more GDO circuits can be implemented in association with one
or more antennas 201, 203, 205, depending upon design
considerations. Note that as utilized herein, the term "oscillator"
may refer to the GDO or GDO circuit itself or may simply refer to
the oscillator component, such as component 306, which makes up one
portion of the overall GDO, such as, for example, GDO 302. Sensors
402, 404, 406 and can be implemented by LC tank sensors, depending
upon design considerations.
FIG. 5 illustrates a block diagram of a multiple sensor system 500
for use in dialysis applications, in accordance with an alternative
first embodiment. System 500 includes multiple GDO circuits 414,
416, 418 (i.e., respectively, GDO1, GDO2, GDO3). Each GDO 414, 416,
418 is analogous to the GDO 302 depicted in FIG. 4. GDO 414 is
connected to a first antenna 408, which in turn is inductively
coupled to a first sensor 402. GDO 416 is connected to a second
antenna 410, which in turn is inductively coupled to a second
sensor 404. GDO 418 is connected to a third antenna 412, which in
turn is inductively coupled to a third antenna 406. GDO 414 is also
connected to ground 415 and to a voltage supply 421. GDO 416 is
connected to ground 417 and also to the voltage supply 421.
Similarly, GDO 418 is connected to ground 419 and to voltage supply
421. The antennas 408, 410 and 412 are analogous to the antennas
201, 203, 205 depicted in FIG. 2(a).
GDO 414 is also connected to a low frequency switch 420, which in
turn can in a closed position permit an electrical connection of
GDO 414 to a processing electronics module 426. Similarly, GDO 416
is connected to a low frequency switch 422, which in turn can in a
closed position permit an electrical connection of GDO 416 to the
processing electronics module 426. Likewise, GDO 418 can be
connected to a low frequency switch 424, which in turn can in a
closed position permit an electrical connection of GDO 418 to the
processing electronics module 426. Note that a pressure output
signal 428 can be obtained from the processing electronics module
426. It is also significant to note that each of the low frequency
switches 420, 422, and 424 can be in some embodiments, perform an
analogous function to the RF switch 228 depicted in FIG. 2(a).
In system 500, multiple GDO circuits 414, 416, 418 are utilized.
Both the GDO circuits 414, 416, 418 and the antenna 408, 410, 412
are always powered up (i.e., oscillations continuously set up in
the circuit and antenna). One or more low frequency switches 420,
422, 424 can be operated by the processing electronics 426, forming
a multiplexer to select the output from each sensor in turn.
In the configuration depicted in FIG. 5, three separate GDO
circuits 414, 416, 418 are respectively associated with three
separate sensors 402, 404, 406. The three GDO circuits 414, 416,
and 418 share the processing electronics module 426. The output
from each GDO 414, 416, 418 can comprise a DC voltage. Thus, the
resulting multiplexer can be composed of low frequency switches
420, 422, 424, which are simple in structure and typically are of a
low cost. It can be appreciated that although only three sensors
402, 404, 406 and three GDO circuits 414, 416, 418 along with three
antenna 408, 410, 412 are depicted in FIG. 4, alternative
embodiments with more or fewer such sensors, antenna or GDO
components may be implemented, depending upon the sensing
application requirements.
Sensors 402, 404, 406 depicted in FIGS. 5 6 and sensors 330, 344
depicted in FIG. 3 can be implemented for example as
inductance-capacitance resonant circuit (LC tank) sensors such as
those disclosed in U.S. patent application Ser. No. 11/242,271,
entitled "Wireless Pressure Sensor and Method Forming the Same."
Alternatively, such pressure sensors can be implemented as wireless
capacitance pressure sensors, such as those described in U.S.
patent application Ser. No. 11/226,085, entitled "Wireless
Capacitance Pressure Sensor.
FIG. 6 illustrates a block diagram of a multiple sensor system 600
for use in dialysis applications, in accordance with another
version of the embodiment depicted in FIG. 5. Note that in FIGS. 5
6, identical or similar parts or elements are generally indicated
by identical reference numerals. System 600 is similar to system
500 depicted in FIG. 5, with some variations to the overall circuit
structure. In the configuration depicted in FIG. 6, the switches
420, 422, and 424 are respectively located between the voltage
supply 421 and respective GDO circuits 414, 416, and 418. Switches
420, 422, and 424 can be implemented as low frequency switches. A
GDO can be selected by powering it up in order to ensure that there
is no interference from a neighboring GDO. Additionally, the power
drawn in the configuration depicted in FIG. 6 may be lower than
that of system 500 illustrated in FIG. 5.
In system 600 depicted in FIG. 6 the GDO circuits 414, 416, 418 can
be powered up in turn by the processing electronics 426, thereby
removing or reducing interference between the antenna 408, 410,
412. The response time of system 600 is however reduced based on
the need for the GDO circuits 414, 416, and/or 418 to warm-up
(i.e., time for oscillations in the GDO's LC oscillator circuit to
build up to their full amplitude).
The various first embodiments of FIGS. 1 6 solve the need for
multiple wireless pressure sensor systems for hemodialysis
applications. Between three and six sensors, for example, can be
utilized to make up the whole range of pressures and locations for
use in a dialysis machine, such as the dialysis machine 110
depicted in FIG. 1. Such sensors can be located on the arterial
line (i.e., after blood out of patient, before blood pump), the
dialyzer line (i.e., after blood pump, before dialyzer), and/or on
the venous line (i.e., after dialyzer, before patient), or any of a
number of other possible locations on or in association with a
dialysis machine or another medical application, such as, for
example, external blood treatment or separation applications.
The typical pressure range over which such sensors (e.g., sensors
402, 404, 406 of FIGS. 5 6) preferably (although not necessarily)
operate is between -700 mmHg and +1000 mmHg. This is, of course,
only a suggested range and other ranges are also possible,
depending upon design considerations and specific application
requirements.
In general, size limitations for sensors utilized in hemodialysis
applications are problematic. It would be beneficial to design a
multiple-sensor system with the lowest cost, small size and fewest
parts. FIGS. 1 6 represent one possible embodiment. A second
embodiment involves the use of wireless LC tank multiple sensors in
the context of a sensor system in which the sensors share a single
antenna. Multiple capacitors can be linked with a single planar
coil, such that each associated variable capacitor results in a
signature frequency (i.e., spurs). Multiple characteristic resonant
frequencies can be detected in such a system through prudent
design.
FIG. 7 illustrates a graph 700 depicting a variety of frequencies
in the context of a sensor system for dialysis applications, in
accordance with a second embodiment. In graph 700, f.sub.0
represents the fundamental frequency of the sensor system that will
not be detected, while f.sub.1, f.sub.2, and f.sub.3 are spurs
related to each sensor in, for example, the three sensor
system.
FIG. 8 illustrates a sensor system 800 based on a plurality of
circular electrodes forming variable capacitors, in accordance with
the second embodiment. In the configuration of system 800, two
sub-systems 802 and 818 are illustrated. Sub-system 802 includes a
group of electrodes 804, 806, 808, while sub-system 818 includes a
group of electrodes 812, 814, 816. In the lower level configuration
of sub-system 802, the three circular electrodes 804, 806, and 808
can be associated with three respective variable capacitors (not
shown in FIG. 8). Each electrode 804, 806, and 808 is connected to
an antenna 810. At the higher level of sub-system 818, the three
electrodes 812, 814, 816 can be located on a pressure diaphragm
(not shown in FIG. 8) and respectively correspond to each electrode
805, 806, 808 of the lower level of sub-system 802. Note that the
dashed line 809 in FIG. 8 represents the interconnection between
sub-systems 802 and 818.
FIG. 9 illustrates a schematic diagram of an example equivalent
circuit 900 of the configuration depicted in FIG. 8. The
configuration depicted in FIG. 9 is presented in order to assist in
explaining the functioning of the configurations depicted in FIG.
7. Note that in FIGS. 7 and 9, the variables f.sub.1, f.sub.2, and
f.sub.3 generally represent the same functionality. In FIG. 9,
R.sub.0, C.sub.0, R.sub.1, L.sub.1, R.sub.2, L.sub.2, R.sub.3 and
L.sub.3 represent small electrical values. Note that equations 902
depicted in FIG. 9 depicted general formulations for determining
f.sub.1, f.sub.2, and f.sub.3. In general, the equivalent circuit
900 can be composed of an inductor 928 connected to a capacitor
926, which in turn is connected to a resistor 924 that in turn can
be connected to ground 930. Similarly, a capacitor 910 is connected
to a resistor 908, which in turn is connected to an inductor 906
that in turn can be connected to ground 930.
A capacitor 916 can be connected to a resistor 914, which in turn
is connector to an inductor 912 that in turn is connected to ground
930. A capacitor 918 can be further connected to a resistor 920
that in turn is connected to an inductor 922. Note that the
inductor 928, and the capacitors 910, 916 and 918 are generally
connected to an antenna 904. FIGS. 8 9 thus generally indicate that
the pressure sensors discussed herein can be implemented in the
context of an LC type sensor (e.g., LC (Inductance-Capacitance)
tank sensor), an RLC (Resistance-Inductance-Capacitance) type
sensor, or a combination thereof, depending upon design
considerations.
It will be appreciated that variations of the above-disclosed and
other features and functions, or alternatives thereof, may be
desirably combined into many other different systems or
applications. Also that various presently unforeseen or
unanticipated alternatives, modifications, variations or
improvements therein may be subsequently made by those skilled in
the art which are also intended to be encompassed by the following
claims.
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